EVIDENCE FROM EVIDENCE FROM GENETICS IIGENETICS II

Genetics After MendelGenetics After Mendel

Are all traits this simple?Are all traits this simple? Some phenotypes are Some phenotypes are

due to the action of a due to the action of a single genesingle gene

MOST, however, are MOST, however, are polygenicpolygenic HeightHeight Skin color Skin color Disease predispositionDisease predisposition

Heart diseaseHeart disease High blood pressureHigh blood pressure DiabetesDiabetes CancerCancer

1) Concept of Polygene 1) Concept of Polygene Inheritance Inheritance =Traits are =Traits are

determined by determined by several genes at several genes at different loci.different loci.

e.g. Human heighte.g. Human height

2) Concept of Multiple Alleles2) Concept of Multiple Alleles Many traits have multiple alleles not just two Many traits have multiple alleles not just two

such as T or t.such as T or t.

e.g. ABO blood type there are 3 alleles = A, B, Oe.g. ABO blood type there are 3 alleles = A, B, O

So: So:

AA, AB, AO, BB, BO, OO = 6 GenotypesAA, AB, AO, BB, BO, OO = 6 Genotypes

3) Concept of Pleiotropy3) Concept of Pleiotropy= Multiple effects caused by = Multiple effects caused by a single genea single gene

e.g. Marfan’s e.g. Marfan’s syndromesyndrome

4) Chromosomes Exist4) Chromosomes Exist(1875)(1875)

When do you see When do you see chromosomes?chromosomes?

First of all you have to First of all you have to use stains for DNA use stains for DNA

ChromosomesChromosomes only in only in condensed form when condensed form when preparing for nuclear preparing for nuclear divisiondivision

Otherwise present as Otherwise present as chromatinchromatin (unraveled) (unraveled)

5) Chromosome Numbers 5) Chromosome Numbers Vary Among SpeciesVary Among Species

AntAnt 22 MosquitoMosquito 66 OrangeOrange 18, 27, 3618, 27, 36 FrogFrog 2626 CoffeeCoffee 4444 Spanish ButterflySpanish Butterfly 380380 Stalked adders tongue 1020 Stalked adders tongue 1020

Human KaryotypeHuman Karyotype= Chromosome Pattern= Chromosome Pattern

6)Chromosomes6)Chromosomes Come in Pairs Come in Pairs

Cell NucleusCELL

6 Chromosomes

3 Pairs

KaryotypeKaryotype= Chromosome Pattern= Chromosome Pattern

Humans Have 46 Chromosomes Humans Have 46 Chromosomes 23 Pairs 23 Pairs

Diploid Number = 46 (2n)Diploid Number = 46 (2n)

Haploid Number = 23 (n)Haploid Number = 23 (n)

Polyploid Numbers = 3n, 4n, 5n,…….etcPolyploid Numbers = 3n, 4n, 5n,…….etc

Humans Have 46 Chromosomes Humans Have 46 Chromosomes 23 Pairs23 Pairs

One set of 23 from fatherOne set of 23 from father

One set of 23 from motherOne set of 23 from mother

Humans Have 46 Chromosomes Humans Have 46 Chromosomes 23 Pairs23 Pairs

22 Pairs are autosomes22 Pairs are autosomes

1 Pair are sex chromosomes1 Pair are sex chromosomes

♀ ♀ = xx ♂ = xy= xx ♂ = xy

Human KaryotypeHuman Karyotype= Chromosome Pattern= Chromosome Pattern Is this from a woman or a man?Is this from a woman or a man?

A)A) WomanWoman

B)B) ManMan

C)C) I don’t knowI don’t know

7) Mendel’s Factors (Genes)7) Mendel’s Factors (Genes) Occur on Chromosomes Occur on Chromosomes

in particular places= in particular places= locuslocus2 Alleles

Homozygous Dominant

Heterozygous

Homozygous Recessive

8) Many Genes Exist on 8) Many Genes Exist on Each ChromosomeEach Chromosome

Viruses = 5 Viruses = 5 10 genes 10 genes

Bacteria = 1,000 Bacteria = 1,000 6,000 genes 6,000 genes

Human = 25,000 genesHuman = 25,000 genes

9) Concept of Linkage9) Concept of Linkage Genes on the same chromosome are linkedGenes on the same chromosome are linked

Do you remember this slide?Do you remember this slide?What if RY are linked together &ry are What if RY are linked together &ry are linked together ?linked together ?

Non Independent Assortment = REDUCED VARIABILITY

9) Concept of sex-linked 9) Concept of sex-linked traits = Traits carried on the traits = Traits carried on the

sex chromosomessex chromosomes Muscular dystrophy Muscular dystrophy Color blindnessColor blindness Pattern baldnessPattern baldness HemophiliaHemophilia All are carried on the X chromosomeAll are carried on the X chromosome

and are displayed in malesand are displayed in males

Because Because ♂♂ only have one X chromosome.only have one X chromosome.

So if they have the allele for the trait, So if they have the allele for the trait, they will show it.they will show it.

10) Cell Division Occurs10) Cell Division Occurs

Each arm is called aEach arm is called a

chromatidchromatid

Step 1: The chromosome duplicateThere are two identical arms on each one.

Cell Division in Body CellsCell Division in Body Cells Step 2: The Chromatids Divide Equally Step 2: The Chromatids Divide Equally

During Cell DivisionDuring Cell Division Division in body (somatic) cellsDivision in body (somatic) cells

46

4646

Mitosis

Daughter cells have

same # chromosomes as parent cell

92

The chromosomes are lined up

The chromatids are pulled apart

46 chromosomes in each cell

Division in Sex Organs Division in Sex Organs (In the Testes) (In the Testes)

46

2323

23232323

4 Sperm

92

Division in Sex Organs Division in Sex Organs (In the (In the Testes) Testes)

46

2323

23232323

4 Sperm

Meiosis =

Reduction Division

Daughter cells with

½ # Chromosomes

As parent cell

Stages of Meiosis Meiosis (in animals) Meiosis (in animals)

produces 4 haploid produces 4 haploid gametes from 1 gametes from 1 diploid celldiploid cell

At the end of the first At the end of the first division (division (Meiosis IMeiosis I) ) the 2 cells are the 2 cells are already haploidalready haploid

The second division The second division ((Meiosis IIMeiosis II) splits the) splits the

2 chromatids2 chromatids

Division in Sex Organs Division in Sex Organs

(In the Ovary)(In the Ovary)

46

23 23

23Egg + 3 Polar

Bodies

Meiosis

Division in Sex Organs Division in Sex Organs

(Testes & Ovaries)(Testes & Ovaries)

46

2323

23232323

4 Sperm

46

23

23Egg + 3 Polar

Bodies

Distribution of Distribution of Chromosomes in gametesChromosomes in gametes

The gametes end up with only one set of The gametes end up with only one set of chromosomes. It is random which chromosomes. It is random which chromosome of a pair goes into which chromosome of a pair goes into which gamete.gamete.

SO, each gamete has a mixture of the SO, each gamete has a mixture of the mother & father’s chromosomes. mother & father’s chromosomes.

This produces enormous gamete variabilityThis produces enormous gamete variability

How many combinations of maternal How many combinations of maternal chromosomes are possible in a human chromosomes are possible in a human egg due to independent assortment egg due to independent assortment during meiosis?during meiosis?

A: 23 combinationsA: 23 combinations

B: 46 combinationsB: 46 combinations

C: 23C: 2322 = 529 combinations = 529 combinations

D: 2D: 223 23 = ~ 8 million combinations= ~ 8 million combinations

The Fate of Genetic Material The Fate of Genetic Material During Sexual ReproductionDuring Sexual Reproduction

You contain You contain genetic material genetic material from both your from both your Mom and Dad.Mom and Dad.

You have 46 You have 46 chromosomes, chromosomes, and so will your and so will your children. children.

9) Concept of Cross-over9) Concept of Cross-over=Sister chromosomes swap=Sister chromosomes swappieces during meiosispieces during meiosis

Now for a StoryNow for a Story

Santhi SoundarajanSanthi Soundarajan

Santhi Soundararajan won Santhi Soundararajan won the silver medal for 800 the silver medal for 800 meters at the 2006 Asian meters at the 2006 Asian Games in Doha, Qatar.Games in Doha, Qatar.

Following her silver medal Following her silver medal performance, her sex performance, her sex was officially questioned.was officially questioned.

http://www.ibnlive.com/videos/28851/how-are-athletes-gender-tested.html

18 Dec. 2006: Indian athlete 18 Dec. 2006: Indian athlete Santhi Soundararajan fails gender Santhi Soundararajan fails gender testtest Sports writer KP Mohan said that a team of Sports writer KP Mohan said that a team of

doctors, including a gynecologist, doctors, including a gynecologist, endocrinologist and psychologist, normally endocrinologist and psychologist, normally examines athletes, and puts them through examines athletes, and puts them through physical and clinical examinations during a physical and clinical examinations during a gender test.gender test.

Santhi Soundararajan's test was done soon after Santhi Soundararajan's test was done soon after Soundararajan came second in the women's Soundararajan came second in the women's 800m race on 9 December but is not clear how 800m race on 9 December but is not clear how she failed the test at the Asian Games in Doha.she failed the test at the Asian Games in Doha.

How is sex determined in humans? How is sex determined in humans?

Anatomy:Anatomy: Primary and secondary sexual Primary and secondary sexual characteristics - genitalia, body hair, pelvis, etc.characteristics - genitalia, body hair, pelvis, etc.

Physiology:Physiology: Function and interaction of the sex Function and interaction of the sex organs including concentrations of sex organs including concentrations of sex hormones such as estrogen, progesterone, and hormones such as estrogen, progesterone, and testosterone.testosterone.

Imagine that you are a member of the committee Imagine that you are a member of the committee assigned to determine whether Santhi is female. assigned to determine whether Santhi is female. Here are possible results of the initial tests (we Here are possible results of the initial tests (we don’t know the real results):don’t know the real results):

Female genitalia: YesFemale genitalia: Yes

Breasts and pubic hair: YesBreasts and pubic hair: Yes

Regular menstrual cycle: NeverRegular menstrual cycle: Never

From this information, you conclude From this information, you conclude that Santhi isthat Santhi is

A: Male B: FemaleA: Male B: Female

Is there another way that sex is Is there another way that sex is characterized in humans?characterized in humans? Chromosomes:Chromosomes:

Females possess two X chromosomes in Females possess two X chromosomes in each of their cells, whereas males have one X each of their cells, whereas males have one X and one Y chromosome.and one Y chromosome.

How is Sex Determined in How is Sex Determined in Humans?Humans?

Sex is determined by Sex is determined by the sex chromosome the sex chromosome carried by the sperm.carried by the sperm.

sperm

eggXX XY

XX XY

girls boys

X

X

Y

X

Suppose this was Santhi’s Suppose this was Santhi’s KaryotypeKaryotype

Would you Would you A) Disqualify herA) Disqualify her B) Let her keep her medalB) Let her keep her medal C) Do more testsC) Do more tests

How is Sex Characterized in How is Sex Characterized in Humans?Humans?

In addition to anatomy, physiology, and In addition to anatomy, physiology, and chromosomes, there is a 4chromosomes, there is a 4thth answer: answer:

Genes:Genes: Specific genes determine Specific genes determine whether an embryo will develop as a whether an embryo will develop as a male or female.male or female.

SRYSRY ( (SSex- Determining ex- Determining RRegion of egion of the the YY chromosome) Gene chromosome) Gene Early in development, the Early in development, the

immature gonads of males and immature gonads of males and females are indistinguishable.females are indistinguishable.

Males: In the 7Males: In the 7thth week of week of development, the SRY gene on the development, the SRY gene on the Y chromosome activates a number Y chromosome activates a number of genes, and the gonads develop of genes, and the gonads develop as testes.as testes.

Females: With no SRY gene, Females: With no SRY gene, gonads develop as ovaries by gonads develop as ovaries by defaultdefault..

Could Santhi have an XX Could Santhi have an XX karyotype and be male?karyotype and be male?

A: No, an XX individual is always female.A: No, an XX individual is always female.

B: Yes, this is common.B: Yes, this is common.

C: Yes, if a male-determining control gene is C: Yes, if a male-determining control gene is carried on one of her X chromosomes.carried on one of her X chromosomes.

What about crossing over ?What about crossing over ?

Crossing overCrossing over can occur anywhere along can occur anywhere along the autosomes.the autosomes.

In males, the sex chromosomes (X and Y In males, the sex chromosomes (X and Y chromosomes) normally cross over only chromosomes) normally cross over only at their tips.at their tips.

BUT sometimes the SRY gene is involvedBUT sometimes the SRY gene is involved

Special note:

It may take a little while for thenext slide to load.

http://www.hhmi.org/biointeractive/media/meiosis-lg.mov

Can you have an XX male or Can you have an XX male or XY female?XY female?

What sex is XX (What sex is XX (SRYSRY+)?+)? What sex is XY (What sex is XY (SRYSRY-)?-)?

Sex reversal occurs in 1 in 20,000 births!Sex reversal occurs in 1 in 20,000 births!

If you were a member of the Asian If you were a member of the Asian Games medal committee, and Santhi’s Games medal committee, and Santhi’s karyotype revealed that she is XY and karyotype revealed that she is XY and SRY-, what would you do?SRY-, what would you do?

A: She has female genitalia, allow her to A: She has female genitalia, allow her to keep her medalkeep her medal

B: She is genetically male, take herB: She is genetically male, take her

medal awaymedal away

C: She has male genitalia , take C: She has male genitalia , take

her medal awayher medal away

What do you think about requiring What do you think about requiring gender testing for female athletes in gender testing for female athletes in international competition?international competition?

A: It should be banned because gender A: It should be banned because gender determination is so complexdetermination is so complex

B: It is necessary to ensure an even playing fieldB: It is necessary to ensure an even playing field

C: It is necessary but needs to include a large C: It is necessary but needs to include a large number of genetic tests to ensure fairnessnumber of genetic tests to ensure fairness

D: It should be required for all athletes, both male D: It should be required for all athletes, both male and femaleand female

What about Santhi What about Santhi Soundararajan?Soundararajan?

Santhi was stripped of her silver medal.

An anonymous official in the know has reported that Ms. Soundarajan's tests revealed more Y chromosomes than are usually present in the genetic make-up of a female. No official statement has been made.

What about Santhi What about Santhi Soundararajan?Soundararajan?

In September 2007, Santhi Soundarajan was reported to have attempted suicide, reportedly by consuming pesticide at her residence.

The attempt was blamed on gender, economic, and sports pressure in India.